Washington is abuzz with the Iran deal, officially known as the Joint Comprehensive Plan of Action (JCPOA), which was agreed upon last month between the P5, Germany and the EU on the one side, and Iran on the other. The intense debate about the merits of the deal will continue until 17 September, when Congress returns from recess and votes on whether to accept or reject the deal. Regardless which way the vote goes—and the odds are that the deal will narrowly survive this vote—this issue will be the defining foreign policy moment of the Obama presidency. The political fall-out of this deal will continue until well beyond September, and will undoubtedly impact on the 2016 presidential race.

The ongoing debate about the JCPOA is really about two things: the first is Iran’s nuclear program and the second is Iran’s behaviour in the Middle East. Unfortunately, the JCPOA only deals with the nuclear side of the equation and doesn’t address the non-nuclear issues. Put differently, Congress is effectively being asked to vote on the merits of the nuclear deal in a geostrategic vacuum.

According to the nuclear experts, this is a good deal and probably the best that one could hope for given the number of participants involved in the negotiations. And while even the supporters of the deal recognise there are weaknesses in the agreement—it delays but doesn’t end Iran’s nuclear program—Iran isn’t required to close any of its nuclear facilities. It also doesn’t include ‘anywhere, anytime’ inspections—but supporters feel it should be accepted by Congress nevertheless.

However, President Obama has had few, if any, wins on the foreign policy front and with less than two years left in his presidency, he’s decided to take no prisoners on this issue. On the contrary, having negotiated what he believes to be one of the most comprehensive nuclear inspection regimes ever agreed to, this is a unique opportunity to leave the Oval Office on a grand note. However, it’s in the selling of the deal to Congress that things have turned nasty.

It’s also important to remember history. Some 35 years ago, when a Democratic president was in the White House, Iranian students sympathetic to Ayatollah Khomenei overran the American embassy in Tehran and held over 50 diplomats hostage for well over a year (444 days to be precise). They were eventually released on the day Ronald Reagan—the Republicans’ ideological hero—was inaugurated president in January 1981. This whole episode was seared in the psyche of the American public and, needless to say, bred deep distrust of the Iranian regime and the mullahs who run it today. Cutting a deal with Iran is something anathema to Republicans. This brings us to the second part of the equation: Iran’s behaviour in the Middle East.

The battlelines have been drawn: all Republican members of Congress as well as a significant number of Democrats, including some prominent ones, have rejected the deal. They’ve done so not only because of its nuclear aspects but because they feel that this deal will still allow Iran to behave in ways that are against American and Israeli interests.

Although not specifically spelled out, there’s a built-in assumption in the Obama administration that this deal will somehow convince the Iranian regime to modify its behaviour in the region. This is wishful thinking. There’s absolutely no reason why Iran should stop supporting Hezbollah in Lebanon, President al-Assad in Syria, Hamas in Gaza, the Shi’ite militias in Iraq and the Houthis in Yemen—they’ve managed to cut a nuclear deal with the international community while doing just that. On the contrary, Iran may well intensify its activities in those areas. And this is what worries the agreement’s opponents.

At this stage, the opponents of the deal don’t have the numbers in both houses to override a presidential veto, but they’ll fight this to the very end. A recent survey suggests that 41% of Americans feel that the Iranians got the upper hand in the agreement.

Accordingly, while the Republicans will most likely lose this battle and the Iran deal will survive a determined Congressional opposition, all Republican candidates for the 2016 presidential race have promised that, were they to be elected president, one of their first executive orders would be to rip up the Iran deal. Let’s watch that space.